T-wave alternans is beat-to-beat alternation in the morphology, amplitude, and/or polarity of the T-wave, and can be observed on surface electrocardiogram (ECG) recordings. T-wave alternans (TWA) has been recognized in a variety of clinical conditions, including acquired and congenital long QT syndrome and ischemic heart disease associated with ventricular arrhythmias. TWA is considered an independent predictor for cardiac arrhythmias. Experimentally, TWA has been shown to be a precursor of ventricular tachycardia.
In past practice, TWA has been assessed from surface ECG recordings obtained in a clinical setting as an indication of the long-term risk for ventricular arrhythmias. A Fast Fourier Transform (FFT) method is used for frequency domain analysis of T-waves, and a Modified Moving Averaging (MMA) method is used for time domain analysis of T-waves. The low-amplitude changes in the T-wave signal during TWA, which is on the order of microvolts, requires complicated software to assess TWA from a surface ECG recording of typically 128 heart beats or more during exercise or high-rate atrial pacing. Such methods require storing and analyzing more cardiac cycles than are typically available in an implantable cardioverter defibrillator (ICD). TWA assessment using fewer cardiac cycles for practical implementation in ICDs for use in short-term prediction of the onset of arrhythmias is needed.